1. Field of the Invention
This invention relates to flame retardant polyorganosiloxane foams.
2. Background Information
Polydiorganosiloxane foams can be rendered flame retardant using materials such as platinum and carbon black that do not evolve noxious or toxic vapors at elevated temperatures. Compositions have been developed which are useful for filling the spaces left through building walls and floors when pipes, electrical conduits, ventilation ducts, and such are installed. These foams are used to fill the spaces so as to prevent the passage of smoke vapors and water in the event of a fire in the building.
An early flame retardant foam was described by Smith in U.S. Pat. No. 3,923,705. issued Dec. 2, 1975. A syntactic polyurethane foam having flexible fibers and microballons to impart a cellular structure was disclosed by Harper in U.S. Pat. No. 4,082,702. issued Apr. 4, 1978. A flame retardant polyorganosiloxane foam containing platinum, finely divided nonmetallic, fibrous heat resistant material and finely divided nonmetallic, cellular heat resistant material is disclosed by Harper in U.S. Pat. No. 4,433,069, issued Feb. 21, 1984.
It has been found that compositions of the type used by Harper in U.S. Pat. No. 4,433,069 are subjected to severe separation of the ingredients upon storage for long periods of time such as several months. The cellular fillers tend to rise to the top while the fibrous and granular fillers tend to fall to the bottom. It is very difficult to remix the compositions once they have separated and is a cause of great concern to the user of the composition. Since the ingredients react to form a foam, it is necessary to store the ingredients as two packages, which are mixed together for use. Both of these packages are subject to settling, which means the user has to mix each package separately, then mix them together in order to produce a useful product.